Slack adjusters are conventional devices incorporated into most railroad truck car brake systems. Such slack adjusters are used to adjust the travel of the air cylinder piston rod and the associated brake beams to compensate for brake shoe wear.
Typically, a slack adjuster is connected between the two brake beams, and is connected for pivoting movement at a terminal end to the brake cylinder rod and one brake beam through a force application lever. As the brake shoes wear due to use, the length which the brake cylinder rod must travel is increased. The slack adjuster, which is typically a spring loaded rod fitted in a cylinder, is also attached to the other brake beam, with the rod serving to actuate its associated brake beam so that both beams move in unison. The slack adjuster rod movement is controlled by a ratchet-pawl type mechanism which locks the rod in place to ensure that equal pressure is delivered all four brake shoes regardless of the wear condition.
Prior art slack adjusters provided no compensation for the vibrational forces which act on the brake cylinder rod during braking operations. As the brake shoes contact the truck car wheels, vibrational force is transmitted to the brake assembly, which causes the cylinder rod to oscillate from side to side. The further the rod is extended due to brake shoe wear, the more vibrational force is transmitted to the rod. Such side-to-side oscillation, even in small amounts, causes cylinder air leakage. If enough air leaks out of the cylinder, braking power is reduced or can be lost totally.